Patent GB-1430227-A (GB)
Title: Transducers
IPC: B06B1/06
Filed: 1973-03-07
Abstract: 1430227 Piezoelectric devices TAGA ELECTRIC CO Ltd 7 March 1973 47490/75 Divided out of 1429856 Heading H4J A transducer arrangement has two electrostrictive elements 60, 61 (Fig. 3) which, when the transducer arrangement is energized at its fundamental resonant frequency, are located at positions of different mechanical stress along the axial direction of the transducer arrangement. The ratio of motional admittance to clamped admittance for the first electrostrictive element is different from the ratio of motional admittance to clamped admittance for the second electrostrictive element. An output signal responsive to motional current which flows through the motional admittance of the transducer is obtained, and this output signal is a difference signal of the two electrostrictive regions, so that the clamped current components flowing through the clamped admittance of the first and second regions cancel each other out. A horn has a smaller diameter cylindrical portion 75, an exponential portion 76 and a larger diameter cylindrical portion 77. A metal body 78 and the portion 77 are held together by a bolt 79 and sandwich between them electrostrictive elements 60, 61 an insulator 64 and electrode plates 62, 63. A differential current transformer 80 has an intermediate tap 82 on primary winding 81 and is connected to one electrode of an energizing power supply 83. The ends of winding 81 are connected to electrode plates 62 and 63 of the transducer. The other electrode of the power supply 83 is connected to metallic body 78. A load 85 connected to the secondary winding 84 permits a signal proportional to the vibrating speed to be obtained. The elements 60, 61 are displaced from a node at the fundamental resonance frequency and the stresses in the elements 60, 61 differ, when the transducer is energized at this frequency, to provide the signal proportional to vibrating speed. In another arrangement (Fig. 1) lead zirconate-lead titanate elements 60, 61 are separated by a resilient insulator 64 interposed between two electrode plates 62, 63. A cylincrical metal body 66 having a bolt 65 and metal body 67 clamp the elements 60, 61 by a washer 68 and nut 69. The ratio of motional admittance to clamped admittance for one element differs from that of the other element. Electrodes 62, 63 are connected to one terminal of the energizing power supply and the metal bodies 66, 67 contacting the other surfaces of the elements 60, 61 are connected to the other terminal of the energizing power supply. The difference between the exciting currents flowing into elements 60, 61 is applied to a bridge circuit or differential current transformer to provide a signal proportional to vibrating speed. Insulator 64 is a thin film of alumina porcelain, beryllia porcelain, or epoxy resin containing copper foil with glass fibre on both surfaces. The resilient insulator 64 may be omitted provided the bolt 65 and body 67 are insulated and there is a single electrode between the elements 60, 61. An alternative arrangement (Fig. 2, not shown) omits the insulator 64 but has four electrostrictive elements arranged so that the polarizing direction of alternate elements is reversed.